⚙️ Lesson 6.1: Managing Processes

What Is a Process?

Every program you run creates at least one process — an instance of a running program with its own memory, open files, and a unique PID (Process ID).

Key concepts:

• PID — a unique number identifying each process. PID 1 is always the init system (systemd on Ubuntu)
• PPID — Parent PID: the process that spawned this one. Your terminal's shell is the parent of commands you type
• State — running, sleeping (waiting for input/events), stopped, or zombie (finished but not yet cleaned up)
• Owner — the user who started the process (affects what it can access)

Viewing Processes with ps

ps shows a snapshot of current processes. It's not real-time — it shows the state at the moment you run it.

# Show processes in the current terminal session
ps

# Show ALL processes (every user, with details)
ps aux

# Show processes in a tree (parent-child relationships)
ps auxf

# Show processes for the current user
ps -u $USER

# Show only specific columns
ps -eo pid,ppid,user,%cpu,%mem,comm --sort=-%cpu | head -20

USER       PID %CPU %MEM    VSZ   RSS TTY   STAT START   TIME COMMAND
root         1  0.0  0.3 169464 13276 ?     Ss   09:00   0:02 /sbin/init
ray       4523  2.1  3.5 345600 142300 ?    Sl   09:15   1:23 /usr/bin/firefox
ray       4891  0.0  0.1  10456  5632 pts/0 Ss   09:20   0:00 bash

# Find all firefox processes
ps aux | grep firefox

# Exclude the grep command itself from results
ps aux | grep [f]irefox

Real-Time Monitoring with top

top is the built-in real-time process monitor — it updates every few seconds (like Task Manager on Windows).

# Launch top
top

# Show only processes for your user
top -u $USER

Navigating Inside top

top - 14:32:10 up  5:32,  2 users,  load average: 0.52, 0.38, 0.31
Tasks: 287 total,   1 running, 286 sleeping,   0 stopped,   0 zombie
%Cpu(s):  3.2 us,  1.1 sy,  0.0 ni, 95.4 id,  0.3 wa,  0.0 hi,  0.0 si
MiB Mem :  15924.3 total,   8234.1 free,   4512.6 used,   3177.6 buff/cache
MiB Swap:   2048.0 total,   2048.0 free,      0.0 used.  10890.2 avail Mem

htop — A Better top

htop is an improved, color-coded, interactive process viewer. It shows CPU and memory usage with visual bar graphs and supports mouse interaction.

# Install htop (if not already installed)
sudo apt install -y htop

# Run it
htop

htop Navigation

Stopping Processes

Sometimes a program freezes or you need to stop a runaway process. Linux uses signals to communicate with processes.

Common Signals

Using kill, killall, and pkill

# Send SIGTERM (graceful exit) — default signal
kill 4523

# Force-kill a stubborn process
kill -9 4523
# or equivalently:
kill -SIGKILL 4523

# Kill ALL processes with a given name
killall firefox

# Kill processes by partial name match
pkill fire

# Kill all processes owned by a user (DANGEROUS!)
# pkill -u username

Keyboard Shortcuts for Active Processes

Background and Foreground Jobs

You can run processes in the background to keep using your terminal while they work.

# Run a command in the background (add & at the end)
sleep 120 &
# Output: [1] 5678  (job number and PID)

# List background jobs in this terminal
jobs

# Bring a background job to the foreground
fg %1      # %1 = job number 1

# Suspend a foreground job with Ctrl+Z, then resume in background
# (press Ctrl+Z while something is running)
bg %1      # resume job 1 in background

# Run a command that survives closing the terminal
nohup long_running_script.sh &
# Output goes to nohup.out by default

Finding Processes

# Find which process is using a specific port
sudo lsof -i :8080
# or:
sudo ss -tlnp | grep 8080

# Find which process has a specific file open
sudo lsof /var/log/syslog

# Find a process by name
pgrep -la firefox

# Count how many instances of a process are running
pgrep -c firefox

# Find the PID of a specific command
pidof bash

# See info about process 1 (systemd)
ls /proc/1/

# What command started it?
cat /proc/1/cmdline

# How much memory does it use?
cat /proc/1/status | grep VmRSS

Exercises

# Start a process
sleep 1000 &
# Note the PID from the output

# Try SIGTERM first
kill PID_HERE

# If it's still running (check with: jobs)
# Force kill:
kill -9 PID_HERE

Knowledge Check

Summary

🚀 What's Next?

Next up: checking your system's disk space, hardware, and resource usage — essential for keeping your Linux system healthy.